Although in use for years, head mounted display (HMD) systems have been the subject of continual development and improvement. Applications of such systems range from flight and weapons control for military aircraft to display systems for games. Of particular interest are displays which combine multiple images. For example, most modern military aircraft use heads-up display technology to superimpose information for a variety of flight and weapons systems over the pilot's natural view of the outside world. This provides the pilot with additional information without requiring that the pilot look down towards the instrument panel. A second use of head mounted systems is for night vision goggles in which the user is presented with both a natural image of the outside world as well as an artificial image in which the light levels have been intensified. A third use for such systems is to provide a pilot or other user with a low resolution, wide field-of-view image of a particular scene combined with a high resolution image of a small section of the same scene. This allows the user to retain knowledge of the overall surroundings while obtaining detailed information about a particular area of interest.
There are two basic approaches to providing a user simultaneously with multiple images. The first or binocular approach presents both eyes of the user with both images. For example, a pilot may use a see-through HMD of this type which allows a natural view of the outside world. The desired additional information is provided using a projected image, typically projected on the pilot's visor. The second or monocular approach provides each eye of the user with different image information. For example, a pilot flying at night can be presented with a natural view as well as a light intensified view, each view being provided to a separate eye. One advantage of this system is that the eye which is not viewing the light intensified scene remains dark adapted.
U.S. Pat. No. 4,037,921 discloses the use of a monocular approach for a night vision apparatus. The apparatus provides two light intensified views of a particular scene. One view is a low resolution, wide-angle view while the other is a comparatively high resolution, narrow-angle view. In order to allow the user to properly combine the images, the two views are of the same overall magnification.
From the foregoing, it is apparent that a compact, lightweight, dichoptic display is desired. This device is of particular interest in the area of head-mounted displays where size and weight are critical factors.